The way of insulínica signalling (IIS) in the differentiation of chaste in mellifera Apis.

Author(s)

Sergio Vicente de Azevedo

• Document type: Master's Dissertation
• Press: Ribeirão Preto.
• Institution: Universidade de São Paulo (USP). Faculdade de Medicina de Ribeirão Preto (PCARP/BC)
• Defense date: 2007-05-14

Examining board members

Klaus Hartmann Hartfelder; Ana Maria Bonetti; Isis do Carmo Kettelhut

• Advisor: Klaus Hartmann Hartfelder

Abstract

The initial stimulus that generates the facultative queen/worker polyphenism in highly social insects is a differential alimentation in the larval stages. It affects the general development of the larvae, as well as the differentiation of organs and systems, especially of the female reproductive system. The insulin signaling pathway (IIS) is one of the main pathways that integrates the general development of animals with their respective nutritional conditions. The aim of this work was to investigate the relationship between IIS and caste differentiation in the honey bee Apis mellifera. Using the available Apis mellifera genome information we annotated genes belonging to this pathway. We noted that there are two genes encoding putative insulin receptors, InR1 and InR2. The transcriptional profiles of these genes were obtained by quantitative RT-PCR of queen and workers larvae, giving special attention the period during which the larval diet changes. These results revealed considerable differences in the temporal patterns and levels of the transcripts of two the insulin receptor genes, InR1 (GB15492) and InR2 (GB18331) between the two castes and during their respective larval development. For queens we noted an interesting modulation in InR1 transcription: in the third larval instar it was about five fold higher than the transcription of InR2, but in the fourth instar both receptors were transcribed at similar levels. This variation in InR1 expression may be related to the protein content of royal jelly offered to the queen larvae in third instar, that is higher than the protein content of the royal jelly offered to fourth larvae instar. For the worker larvae samples we observed that transcripts levels of the two receptors, InR1 and InR2, were low in the third larval stage and increased in parallel until the onset of the fifth larval stage. This may have been due to some compound in the worker jelly which stimulates the transcription of both genes coding for insulin receptors. Complementary analysis of transcription levels of InR1 and InR2 were performed on ovaries of queen and worker larvae, and on adult workers maintained on different diets. These complementary analyses highlighted that transcription of the InR genes in the larval ovaries of Apis mellifera was differed from the whole body samples. In adult workers the expression of InR1 was dominant over InR2 during most of the adult life cycle, an inversion was only seen in 13 to 15 days old bees. Furthermore, a positive relationship between protein content and InR1 transcription was observed when analyzing its transcription in adult workers fed with bee bread, a protein-rich diet. The results of this work, in conjunction with those of Wheeler et al. (2007), Seehus et al. (2006) and Patel et al. (2007), are the first information on the IIS pathway in honey bees and they represent the basis for an in-depth pursuit on the relationship between diet and downstream signallng envolved in caste determination and differentiation. (AU)